In general, filled polymer materials are desirable for use in a variety of applications, such as consumer products and polymer composite building materials. Filled polymer materials often employ colorants to improve the appearance and aesthetic character of the objects into which they are formed. Typically, pigments or dyes are added to the polymer before it is blended with the filler. However, colored filled polymer materials are known to fade and undergo aesthetically displeasing color changes. One form of aesthetically displeasing color change is known as “whitening”. When objects formed from colored filled polymer materials are exposed to physical damage, such as scratching, impact, and bending, they are known to change to a white color. The typical mineral fillers that are used are white in color and it is generally understood that the whitening is a result of the white filler becoming exposed at the surface of the object.
In U.S. Pat. No. 7,863,369 Bianchi et al disclose a colored filled polymer material formed of a polymer matrix and a pigment. The pigment includes alumina hydrate particulate having a dye covalently bonded to the surface of the alumina hydrate particulate. However, materials made according to the disclosure of Bianchi are known to blotch and whiten to an unacceptable degree.
Accordingly, there is a continued need within the industry to provide colored filled polymer materials having improved resistance to whitening due to physical damage.
In addition, dispersion of traditional pigments with polymer materials is difficult. Poor dispersion leads to swirling and color variability with the colored polymer material. Further, poor dispersion of the pigment within the plastic article may lead to undesirable mechanical properties. As such, compatibilizers are typically used to disperse pigment within a polymer material. Such compatibilizers include a variety of organic compounds that aid in dispersing the pigment. However, compatibilizers typically are expensive and may also negatively influence mechanical properties of the filled polymer material. In addition, pigments are dispersed in liquid prepolymer mixture using high shear mechanical processes which negatively impact the prepolymer and require the prepolymer mixture to be deaerated.
In Japanese Patent Application Publication Number 1987030133(A), Kaide discloses a colored resin composite made from abundant blending of colorant with a hydrate of metal oxide beforehand, from which damaged parts do not experience a whitening phenomenon. However, Kaide discloses a colored hydrate of a metal oxide that is blended with a high molecular weight plastic or rubber material to yield a composite. The present invention is a filler modified with particles with an association that is strong enough to withstand subsequent processing, in particular suspension and mixing in a polar liquid medium (e.g. methyl methacrylate). A polar liquid media provides a more aggressive environment than the one disclosed in Kaide, and therefore a more challenging one for modified filler to persist.
Accordingly, there is a continued need within the industry for improved dispersion of colorants and fillers in filled polymer materials wherein the filler and modifying materials will withstand processing forces.